The use of planetary gears in the construction of motor vehicles is generally already known. Helically cut planetary gears clearly have a lower noise level compared to planetary gears with straight cut teeth, and this becomes more and more important in view of the increasingly stricter regulations for noise protection.
It is also an advantage of the simply helically cut design that external axial forces are not transmitted to the gearing as a result of heat expansion or clutch thrust. Therein resulting in a smaller total gear width and thus less expensive forging blanks.
The expensive production and assembly of helically cut planetary gears, as well as the prevalence of strong axial forces resulting from the helically cut teeth are problematic. Said axial forces severely strain adjacent parts such as the drive shaft and the output shaft. At the same time high tipping torques also act on the planetary gears considerably straining the radial bearings. Due to the free axial forces from the teeth it is not possible to vary the helical angles, since the forces upon the axial thrust bearings otherwise become too strong. In simple helically cut teeth, the helix angles usually fluctuate between from ten to fifteen degrees. No great overlap ratio takes place due to the small helix angles. Additionally, the required axial thrust bearings cause elevated storage losses and poorer efficiency.
German Patent 401,652 has disclosed a spur-gear drive having a simple helical cut in which a thrust ring which rotates at the same time is provided for absorbing the axial thrusts. Different arrangements of the thrust ring are provided. One of which is designed so as to absorb axial thrusts not only in one direction, but also able to absorb axial thrusts in both directions by situating on one ring pressure surfaces opposite to each other. Occurring impacts can be absorbed by elastic elements between thrust ring and gear, for example, by resilient design of the thrust rings or by elastic intermediate elements.
German Patent 28 15 847, for example, has disclosed the following as methods for mounting the thrust rings:
1. The thrust ring is screwed on the face end. This type of mounting is possible only in gears having relatively large pinions (small reduction ratio), since the inwardly reaching flange of the thrust ring requires additional space. PA0 2. The thrust ring is shrunk fit without additional security against displacement. For sufficient security against slippage, this type of mounting requires, together with strong shrinking compression, large widths of the shrinking ring. This is necessary in the case of high speeds due to the reductions of compression appearing here as consequence of the expansion of the ring. But large thrust ring widths produce disadvantageous enlargements of the widths of the wheel set and gear. PA0 3. The thrust ring is shrunk fit upon the shaft. But is additionally secured by a divided ring and guard ring. Said additional security act, against the insecurity of the slip joint and against unfavorable stress of the thrust ring caused in spur-gear transmissions by the eccentric application of force of the axial thrust. Security elements are usually nuts, guard rings, two-part spacers with added guard ring and radial pins, the same as screws. Experiences with screwed-on thrust rings have shown, together with the disadvantage of a constructionally expensive design, that it is necessary to carry out the fine processing (grinding) of the thrust faces of the thrust ring only after the shrink fitting operation, as otherwise an impact-free motion of the pressure faces is not ensured due to the misalignment of the thrust ring produced during the shrinking operation. This requirement is detrimental to production from industrial and economic points of view. PA0 4. The thrust ring rests upon the shaft with a transitional or light press fit and is joined to the shaft by electron-beam welding to form a one-piece homogeneous unit.
DE-OS 42 16 397 describes a planetary gear with helical cut design, particularly for motor vehicles, which is provided with a sun wheel non-rotatably connectable with a drive shaft, a plurality of planet gears mounted on a planet carrier and surrounding the planet gears a ring gear which is connected with a ring-gear carrier. For absorbing axial forces there are provided between the sun wheel and the planet gears and between the planet gears and the ring gear thrust rings which are placed on the face ends of the respective gears. The thrust rings are situated on both sides of the planet gears in order to absorb the axial forces both in push and pull directions. This means an expensive assembly due to the arrangement of four pairs of pressure surfaces and at the same time elevated cost, since the pressure surfaces must be carefully and expensively manufactured to obtain a secured lubricant wedge therebetween. The thrust rings are here welded on both sides on the sun wheel.